1. Field of the Invention
The present invention relates generally to sensor arrays for acoustic sensing systems.
2. Description of the Related Art
Fiber optic interferometric sensors shows promise in applications in which size, electrical interference, and electromagnetic detection make electronic sensors impractical. Such interferometric sensors are capable of measuring a parameter (i.e., a measurand) with a very high dynamic range (e.g., 120 dB) and have been used in acoustic sensing applications, for example. Fiber optic sensors are supplied optical signal power by signal sources, and their output is detected by receivers. As a practical matter, however, the distance separating the sensors from the signal sources (and the receivers) is limited by optical loss at the signal wavelength and by non-linear optical effects related to the signal light. Thus, it is difficult to construct an optical sensor architecture in which the distance separating the sensor (or sensors) from the optical signal source is very large.
One preferred embodiment of the invention is an optical sensor architecture which receives an input optical signal from a signal source and which outputs a perturbed optical signal to a receiver. The architecture comprises at least one sensor which receives the input optical signal and which outputs the perturbed optical signal. A signal distribution fiber is disposed between the sensor and the signal source to distribute the input optical signal to the sensor. A return fiber is disposed between the sensor and the receiver to couple the perturbed optical signal from the sensor to the receiver. An optical amplifier is positioned along the return fiber at an optical distance at least 10 kilometers from the receiver. The optical amplifier amplifies the perturbed optical signal propagating to the receiver.
Another embodiment is an optical sensor architecture which receives an input optical signal from a signal source and which outputs a perturbed optical signal to a receiver. The architecture comprises at least one sensor which receives the input optical signal and which outputs the perturbed optical signal. A signal distribution fiber is disposed between the signal source and the sensor to distribute the input optical signal to the sensor. A return fiber is disposed between the sensor and the receiver to couple the perturbed optical signal from the sensor to the receiver. The architecture further includes first and second optical amplifiers positioned along the return fiber at an optical distance at least 10 kilometers from the receiver. The first and second optical amplifiers receive and amplify the perturbed optical signal. The amplified perturbed optical signal is sent to the receiver. The first amplifier is located between the second amplifier and the sensor in the optical path. The architecture also includes at least one pump distribution fiber for pumping the amplifiers. The at least one pump distribution fiber is coupled to at least one pump source.
Yet another embodiment is an optical sensor architecture which receives an input optical signal from a signal source and which outputs a perturbed optical signal to a receiver. The architecture comprises at least one sensor which receives the input optical signal and which outputs the perturbed optical signal. A signal distribution fiber is disposed between the sensor and the signal source to distribute the input optical signal to the sensor. An optical amplifier is positioned along the signal distribution fiber at an optical distance at least 10 kilometers from the signal source for receiving and amplifying the optical signal. A return fiber is disposed between the sensor and the receiver to receive the perturbed optical signal. An optical amplifier is positioned along the return fiber at an optical distance at least 10 kilometers from the receiver for receiving and amplifying the perturbed optical signal. The amplified perturbed optical signal is sent to the receiver. At least one pump distribution fiber is interposed between at least one optical pump source and at least one of the signal distribution fiber amplifier and the return fiber amplifier.
Another embodiment is an optical sensor architecture which receives an input optical signal from a signal source and which outputs a perturbed optical signal to a receiver. The architecture comprises at least one sensor which receives the input optical signal and which outputs the perturbed optical signal. A signal distribution fiber is disposed between the sensor and the signal source to distribute the input optical signal to the sensor. An optical amplifier is positioned along the signal distribution fiber at an optical distance at least 10 kilometers from the signal source for receiving and amplifying the optical signal. A return fiber is disposed between the sensor and the receiver to receive the perturbed optical signal. The architecture further includes first and second optical amplifiers positioned along the return fiber at optical distances at least 10 kilometers from the receiver for receiving and amplifying the perturbed optical signal. The amplified perturbed optical signal is sent to the receiver. The first optical amplifier is located between the second amplifier and the sensor in the optical path. The architecture fturther comprises at least one pump distribution fiber between at least one optical pump source and at least one of the signal distribution fiber amplifier and the return fiber amplifiers.
Another embodiment of the invention comprises a method for distributing an input optical signal to and returning a perturbed optical signal from a sensor located at tens of kilometers from an optical signal source, an optical pump source, and an optical receiver. The method comprises outputting the optical signal from the optical signal source to an optical signal distribution fiber. The optical signal has a signal wavelength and a signal power level. The signal power level is selected to be approximately at or below a stimulated Brillouin scattering (SBS) threshold of the optical signal distribution fiber. Optical pump light is output from the optical pump source to an optical pump distribution fiber. The optical pump light has a pump wavelength and a pump power level. The pump power level is selected to be at a power level at or below a stimulated Raman scattering (SRS) threshold of the optical pump distribution fiber. The method also includes coupling a distribution amplifier to the signal distribution fiber and the optical pump distribution fiber. The amplifier has a gain when pumped by the pump light to amplify the optical signal to provide an amplified optical signal. The distribution amplifier is positioned at a distance from the optical pump source and the optical signal source so that the pump light and the optical signal have respective power levels at the distribution amplifier such that the distribution amplifier outputs the amplified optical signal at a power level approximately at or below the SBS threshold. The amplified optical signal is coupled to a sensor. The sensor perturbs and amplifies the optical signal and produces a perturbed optical signal on a return fiber. The perturbed optical signal is propagated to the optical receiver.